The operation of cupolas with acid slags has, as its principal objective, the production of low cost irons. The acid cupola is used extensively for making grey cast iron; greater consistency of the charge materials reduces the risk of chemical variations within the metal produced. Nonetheless, there are certain problems associated with current acid operated cupolas. Although fluidity of the slag is generally adequate, there is the need for use of secondary or special fluxes and for this the prior art has traditionally turned to fluorspar. Fluorspar creates hydrofluoric acid, formed as a reaction gas in the cupola which deteriorates fiberglas-type bags utilized to collect residue and particles in the cupola effluent. Even those instances where the cupola does not require a bag house assessory, there is a problem in recycling the transport water used in the slag sluice for conveying the slag. Both iron and fluoride compounds can form on the shell of a water cooled cupola in which the cooling water is rendered acidic by fluoride ions. This coating of the shell limits heat transfer and can result in shell buckling and subsequent cost/operating problems. Fluorspar has become an extremely expensive material primarily because it is imported and is in high demand accompanied by relatively low supply. Accordingly, there is a need to achieve equivalent slag characteristics by the use of slag constituents that do not depend upon fluorspar.
There is still another need that is not satisfied by the use of fluorspar as a fluidizer in an acid-type slag composition and that is the requirement for achieving a good chill factor in the production of grey cast iron.